Examinando por Autor "Requeña Torres, M. A."

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Acceso Abierto
On the Effects of UV Photons/X-Rays on the Chemistry of the Sgr B2 Cloud
(The Institute of Physics (IOP), 2020-05-26) Armijos Abendaño, J.; Martín Pintado, J.; López, E.; Llerena, M.; Harada, N.; Requeña Torres, M. A.; Martín, S.; Rivilla, V. M.; Riquelme, D.; Aldas, F.; Comisión Nacional de Investigación Científica y Tecnológica (CONICYT); European Research Council (ERC); Armijos Abendaño, J. [0000-0003-3341-6144]; Llerena, M. [0000-0003-1354-4296]; Martín, S. [0000-0001-9281-2919]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
The lines of HOC+, HCO, and CO+ are considered good tracers of photon-dominated regions (PDRs) and X-ray-dominated regions. We study these tracers toward regions of the Sgr B2 cloud selected to be affected by different heating mechanisms. We find the lowest values of the column density ratios of HCO+ versus HOC+, HCO, and CO+ in dense H ii gas, where UV photons dominate the heating and chemistry of the gas. The HOC+, HCO, and CO+ abundances and the above ratios are compared with those of chemical modeling, finding that high-temperature chemistry, a cosmic-ray ionization rate of 10(-16) s(-1), and timescales >10(5.0) yr explain well the HOC+ abundances in quiescent Sgr B2 regions, while shocks are also needed to explain the highest HCO abundances derived for these regions. The CO+ is mainly formed in PDRs, since the highest CO+ abundances of similar to(6-10) x 10(-10) are found in H ii regions with electron densities >540 cm(-3) and CO+ emission is undetected in quiescent gas. Among the ratios, the HCO+/HCO ratio is sensitive to the electron density, as it shows different values in dense and diffuse H ii regions. We compare SiO J = 2-1 emission maps of Sgr B2 with X-ray maps from 2004 and 2012. One known spot shown on the 2012 X-ray map is likely associated with molecular gas at velocities of 15-25 km s(-1). We also derive the X-ray ionization rate of similar to 10(-19) s(-1) for Sgr B2 regions pervaded by X-rays in 2004, which is quite low to affect the chemistry of the molecular gas.
Restringido
Structure and kinematics of shocked gas in Sgr B2: further evidence of a cloud–cloud collision from SiO emission maps
(Oxford Academics: Oxford University Press, 2020-10-09) Armijos Abendaño, J.; Banda Barragán, W. E.; Martín Pintado, J.; Dénes, H.; Federrath, C.; Requeña Torres, M. A.; Deutsche Forschungsgemeinschaft (DFG); Australian Research Council (ARC); Banda Barragán, W. E. [0000-0002-1960-4870]; Denes, H. [0000-0002-9214-8613]; Federrath, C. [0000-0002-0706-2306]; Unidad de Excelencia Científica María de Maeztu Centro de Astrobiología del Instituto Nacional de Técnica Aeroespacial y CSIC, MDM-2017-0737
We present SiO J = 2-1 maps of the Sgr B2 molecular cloud, which show shocked gas with a turbulent substructure comprising at least three cavities at velocities of [10, 40] km s(-1) and an arc at velocities of [-20, 10] km s(-1). The spatial anticorrelation of shocked gas at low and high velocities, and the presence of bridging features in position-velocity diagrams suggest that these structures formed in a cloud-cloud collision. Some of the known compact HII regions spatially overlap with sites of strong SiO emission at velocities of [40, 85] km s(-1), and are between or along the edges of SiO gas features at [100, 120] km s(-1), suggesting that the stars responsible for ionizing the compact HII regions formed in compressed gas due to this collision. We find gas densities and kinetic temperatures of the order of n(H2) similar to 10(5) cm(-3) and similar to 30 K, respectively, towards three positions of Sgr B2. The average values of the SiO relative abundances, integrated line intensities, and line widths are similar to 10(-9), similar to 11 K kms(-1), and similar to 31 km s(-1), respectively. These values agree with those obtained with chemical models that mimic grain sputtering by C-type shocks. A comparison of our observations with hydrodynamical simulations shows that a cloud-cloud collision that took place less than or similar to 0.5 Myr ago can explain the density distribution with a mean column density of (N) over bar (H2) greater than or similar to 5 x 10(22) cm(-2), and the morphology and kinematics of shocked gas in different velocity channels. Colliding clouds are efficient at producing internal shocks with velocities similar to 5-50 km s(-1). High-velocity shocks are produced during the early stages of the collision and can readily ignite star formation, while moderate- and low-velocity shocks are important over longer time-scales and can explain the widespread SiO emission in Sgr B2.